usb: cdns3: gadget: fix state inconsistency on gadget init failure

When cdns3_gadget_start() fails, the DRD hardware is left in gadget mode
while software state remains INACTIVE, creating hardware/software state
inconsistency.

When switching to host mode via sysfs:
echo host > /sys/class/usb_role/13180000.usb-role-switch/role

The role state is not set to CDNS_ROLE_STATE_ACTIVE due to the error,
so cdns_role_stop() skips cleanup because state is still INACTIVE.
This violates the DRD controller design specification (Figure22),
which requires returning to idle state before switching roles.

This leads to a synchronous external abort in xhci_gen_setup() when
setting up the host controller:

[ 516.440698] configfs-gadget 13180000.usb: failed to start g1: -19
[ 516.442035] cdns-usb3 13180000.usb: Failed to add gadget
[ 516.443278] cdns-usb3 13180000.usb: set role 2 has failed
...
[ 1301.375722] xhci-hcd xhci-hcd.1.auto: xHCI Host Controller
[ 1301.377716] Internal error: synchronous external abort: 96000010 [#1] PREEMPT SMP
[ 1301.382485] pc : xhci_gen_setup+0xa4/0x408
[ 1301.393391] backtrace:
...
xhci_gen_setup+0xa4/0x408 <-- CRASH
xhci_plat_setup+0x44/0x58
usb_add_hcd+0x284/0x678
...
cdns_role_set+0x9c/0xbc <-- Role switch

Fix by calling cdns_drd_gadget_off() in the error path to properly
clean up the DRD gadget state.

Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Cc: stable <stable@kernel.org>
Signed-off-by: Yongchao Wu <yongchao.wu@autochips.com>
Acked-by: Peter Chen <peter.chen@kernel.org>
Link: https://patch.msgid.link/20260401001000.5761-1-yongchao.wu@autochips.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>